This invention relates generally to airsprings and in particular to fully molded, beadless, flexible rubber members used in airsprings requiring zero pressure roll capability.
Conventionally known airsprings can be classified in several ways. The first classification is by form. Rolling lobe, bellows and sleeve type airsprings are representative of this classification. Secondly airsprings may be classified by the manner in which they are attached to the rigid retainers or pistons of the airspring assembly. In this classification there are beaded forms of airsprings and beadless. The terms "beaded" and "beadless" refer to presence or absence respectively, of a non-extensible, nonductile bead wire or assembly in the cured flexible member. The third classification system is directed to the nature of the flexible member of the airspring assembly. This flexible member may be a sleeve type or a fully molded membrane. The fully molded type is one which assumes a natural molded shape even when the airspring has no internal pressure. Generally the molded shape is of non-uniform radial diameter along the axial length of the airspring. The non-molded type of airspring member is a uniform diameter tubular structure which collapses axially downward on itself when there is a zero pressure condition inside of the airspring.
It is clear that the above-described classification systems overlap and in fact it is felt that nearly every airspring configuration could be classified in all three systems. Prior to this invention all fully molded airspring flexible members were of the bead construction. This is understandable in view of the necessary function which the bead structure has always served in the molding process. The bead is seated in the mold recesses provided and established (1) the internal air seal and (2) the exact axial spacing between the beads of the finished airspring. The seating of the beads of the uncured preform sleeve in the mold recesses is necessary to securely hold the sleeve in position in the forming mold during the application of very high pressures in the interior of the airspring during cure. These pressures are necessary for radial deformation of the fabric reinforced uncured preform. The oppositely laid bias fabrics of the uncured preform sleeve pantograph during the internal pressurization and create great axial stresses downward on the bead area of the preform. The placement of the beads in the provided recesses of the mold resist these axial stresses during the forming portion of the vulcanization step.
This invention provides for the first time a method of molding flexible members to exact molded configurations without the requirement that beads be built into the axially extreme ends of the flexible member. The elimination of internally molded beads in fully molded membranes results in substantial economies derived primarily from (1) elimination of the requirement that only a single flexible member preform may be built at a time, (2) eliminates the time and extra material involved in placing the beads and turning up the fabric over the beads, (3) more than one flexible member may be cured in the same mold from a single preform.
In addition to the economies described above the airspring made with this beadless fully molded flexible member has improved flexing function due to the elimination of the bead turnup area and the resulting localized stresses which develop in this heavily reinforced overlapped area during service. Secondly, a uniform wall thickness is achieved since no bead turnup is required. This uniformity of wall thickness assures a smooth spring rate curve even at the extreme ends of the loading cycle of the airspring.
The terms upper, lower, top, bottom, outward and inward are all oriented by reference to the figures. The terms axis, axial or coaxial always refer to an axis of symmetry or rotation of the mold, membrane or finished airspring.